Internal combustion engines operating with more than one fuel are known. Certain engines use two or more fuels having different reactivities. One example of such an engine is described in U.S. Patent Application Pub. No. 2011/0192367, which was published on Aug. 11, 2011 to Reitz et al. (hereafter, “Reitz”), herein incorporated by reference in its entirety. Reitz describes a compression ignition engine that uses two or more fuel charges having two or more reactivities to control the timing and duration of combustion. According to Reitz, the two fuels are introduced into the combustion chamber at different times to produce stratified regions having different reactivities that will auto-ignite under compression. Controlling the timing of the injections can determine the location of the stratified regions at the time of combustion and can provide for more thorough and complete combustion of the two fuels. Fuel efficiency can therefore be improved and, as an ancillary benefit, emission byproducts of the combustion cycle can be reduced.
One drawback of the two-fuel system described in Reitz is that two fuel reservoirs or sources must be included with the internal combustion system. Operators of the two-fuel internal combustion system, whether it be utilized on a vehicle such as a truck or locomotive or as a stationary application such as an engine for a compressor, must periodically replenish two fuel reservoirs rather than one as is commonly done with more typical internal combustion engines. Moreover, supplies of two fuels with different reactivities may not be readily available or may be cost prohibitive. Such concerns have impeded the application of the two-fuel internal combustion system and the benefits of such systems have thus far not been widely realized.